1. Technical Field
The present invention relates to topical compositions to improve visual acuity and to methods for their use. More particularly, but not exclusively, it relates to eye-drops and the like to ameliorate the effects of presbyopia, myopia, hypermetropia. astigmatism and combinations thereof.
2. Background of Related Art
One prevalent form of visual defect is presbyopia, in which the lens of the eye becomes relatively rigid, particularly with age, so that it becomes increasingly difficult to focus. This leads to eyestrain, and ultimately to recession of the near point, such that a sufferer of presbyopia may be unable to read or work on objects at arm's length.
The conventional response to presbyopia is the use of reading glasses of appropriate strength to move the wearer's near point sufficiently close to allow clear vision at convenient reading and working distances. However, since this will probably also move the wearer's far point closer, sacrificing their distance vision, reading glasses must usually be removed for driving, for example.
Alternatively or additionally, reading glasses are produced whose lenses cover only a small portion of the visual field, so that the wearer may look round them for distance vision. However, the field covered by the lenses may not be sufficient for all purposes.
Bifocal spectacles comprise lenses having zones of different curvatures (or refractive indices), one zone producing a close-in near point for reading, etc, and the other producing a far point at or near infinity for distance work. Varifocal lenses are similar, but with the zones graduating into one another, rather than having a sharp division. Again, the restricted field covered by the “reading” portion of the lens may not be satisfactory, and many people cannot get used to bifocal lenses. Bifocal lenses are usually more expensive than standard lenses.
Furthermore, many people dislike wearing any form of spectacles for reasons of comfort or for reasons of personal style. Contact lenses have been proposed that are akin to bifocal spectacle lenses, but many people are uncomfortable with wearing contact lenses.
Surgical interventions include laser surgery to change corneal curvature, and intraocular implants. Many sufferers from presbyopia would not be prepared to risk (or pay for) corrective surgery.
There are thus drawbacks with each of the known approaches for improving a presbyope's ability to see nearby objects.
Myopia is a visual defect in which the cornea is too steeply curved, or the eyeball is too long, for light from significant distances to be focused on the retina, irrespective of the performance of the lens. A sufferer from myopia thus has a far point closer than infinity, conventionally known as “short sight”. The converse defect is hyperopia or hypermetropia. in which the cornea is too flat, or the eyeball too short, for light from nearby objects to be focused on the retina (again, irrespective of the condition of the eye lens). This leads to a near point a significant distance from the eye, and similar problems to those resulting from presbyopia.
Myopia and hypermetropia may be corrected with spectacles or contact lenses of appropriate curvature, or by surgical intervention, akin to the approaches described above in respect of presbyopia. However, the same drawbacks are also experienced.
Similar drawbacks are found in existing approaches to correcting various other minor refractive errors of the eye. A further complication is that it is not uncommon to suffer from more than one vision defect; for example, a degree of astigmatism is often present for myopes and hypermetropes.
It is hence an object of the present invention to provide a means for improving close-in vision for those suffering from presbyopia or hypermetropia. and/or for improving distance vision for those suffering from myopia, that is simple, convenient and comfortable to use and which obviates the disadvantages of existing approaches. It is also an object of the present invention to provide a means for ameliorating refractive errors of the eye that has the same benefits and/or obviates the same disadvantages. It is a preferred object of the present invention to provide a means of addressing multiple vision problems at once. It is a further object of the present invention to provide a method for ameliorating the effects of presbyopia, myopia, hypermetropia and/or refractive error.